AMD vs Intel memory managemement

Mon Jun 3 13:46:36 MST 2013

Your explanation seems about right to me. The problem though, with a single 
processor with multiple cores, they are all using the same memory interconnect. 

While in theory, and quite possibly in true NUMA systems, this is a more efficient 
way to handle memory management with tasks assigned to a specific processor ( I 
would imagine this would be huge for VM hosts ) but as far as I know, there are no 
real world examples or tests that show this actually works any faster with multiple 
cores. 

But why does CentOS not register all of my memory? Why less than 3/4 of it? I have 
actually had my machine swap due to the work load where as if it had access to the 
other 3 GB of ram it would not have swapped!

Maybe I should have gone with a single 8GB stick of ram instead of dual 4GB. Silly 
me!

Nathan

On Monday, June 03, 2013 13:27:18 Nadim Hoque wrote:

If i recall AMD started doing NUMA which each core gets a dedicated amount of 
memory that is tied to it. The plus side is that when the core needs something in 
its own memory region it does not need to put the request in the queue like in 
non-numa and gets it faster. The down side is if it needs data in a memory region 
that belongs to another core it will take longer since it essentially has to ask that 
core for that data. In non-numa architecture the entire memory space is allocated 
to all cores which means that each core can access memory with out asking 
another for data. The problem with this is that all memory requests is put in a 
queue and the core has to wait until the memory controller is able to process the 
request.  For many core and lot of memory systems you are mostly better off with 
NUMA. Correct me if I am wrong though.

On Mon, Jun 3, 2013 at 7:25 AM, Stephen <cryptworks at gmail.com[1]> wrote:

Not really, Dual channel mode means you can read and write to both Banks of 
memory at the same time (aka Ganged). Single Channel means you treat all ram as a 
single bank reading and writing to one and then the other. think Raid 0 vs JBOD if 
that helps. 
I personally have had 0 issue with greater than 4 GB of ram in a machine with Linux 
and a 64 bit kernel. and i have worked with multiple distributions over the years 
back and forth.
the main difference between Intel and AMD i have seen since the core i series CPUs 
were released is that AMD still has wicked fast memory performance but Intel wins 
most everything else. 

If you have multiple processors you will want to look for numa. This allows inter 
processor communication for ram access. 
It should not matter if you are running ganged or unchanged your is should see all 
ram installed with the exception of the PCI/pcie/chip set nibbling 100 to 700mb 
for doing its thing in consumer chipsets.

On Mon, Jun 3, 2013 at 6:36 AM, keith smith <klsmith2020 at yahoo.com[2]> wrote:

*Mon, 6/3/13, Nathan England /<nathan at nmecs.com[3]>/* wrote:

_nathan at nmecs.com_>Subject: Re: AMD vs Intel memory managemementTo: "Main 
PLUG discussion list" <plug-discuss at lists.phxlinux.org[4]>Date: Monday, June 3, 
2013, 1:35 AM

Yeah, it's a wonderful thing AMD calls "unganged" mode. I have 8 GB of ram in my 
server and the motherboard has enabled "unganged" mode to be more efficient. 
CentOS only recognizes 5.8 GB of ram and I cannot turn off unganged mode. 

I love it...

</sarcasm>

On Sunday, June 02, 2013 17:46:19 keith smith wrote:

-- 

Regards,

Nathan England

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NME Computer Services http://www.nmecs.com[5]
Nathan England (nathan at nmecs.com[3])
Systems Administration / Web Application Development
Information Security Consulting
(480) 559.9681[6]

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